Peter Fleury wrote such a library for general AVR MCUs. One example is a fast (and light-weight) bit-banging I2C library that runs also on MCUs without I2C hardware. The typical use case for assembly programming is when tight timing constraints have to be met. Let’s have a look at these situations and see what one can do. I also give an example of how to pass parameters and get a result from an Assembler function.Although the typical Arduino programmer is probably not interested in writing assembly code, in some situations assembly programming is essential. Like the example below, you can start with just two lines of assembler that fit into a larger program if you wanted to.įollowing are the instructions for creating a mixed C / Assembler program in Arduino. Why? Because since you can mix C / C++ code with the Assembler code this means that you do not have to write a complete assembler program that manages all of the hardware initialisation nitty gritty - you can start small and expand your assembler as and when you you feel comfortable or need to do so. This makes it easy to get started with Assembler while still retaining the familiarity of the Arduino IDE. There are also a couple of ways of including assembler code right inside your Arduino IDE.īy including the assembler in the Arduino IDE, the assembler source is assembled and linked into your project and uploaded to your Arduino from within the IDE - just like any other program. The clock runs on 16MHz, so you can do the math to calculate, how long 1 "nop" needs, and then calculate, how many of them you need). ( very "nop" will need 1 clock cycle - credits to Ghanima for searching that up). You would have to write a loop, that will execute a high number of times. If you don't want to do this, you might get away with executing a high number of "nop" operations (which does nothing). Basically it involves setting the Timers SFRs to the wanted values. If you google for something like "arduino assembler blink" you will also find an example, which configures the timer for blinking. Then you can use this to write a value to an output pin.įor blinking you need a timer. Then write code to write the correct value to the corresponding DDRX bits to set the LED pins to output. You can learn it from the linked example, or from tutorials over the internet. Learn how to set single bits in a byte (in a SFR). For these things, the datasheet of the microcontroller (here the Atmega328P) is a must read (meaning: not completely, but enough to feel comfortable getting needed information from it). The current state (LOW or HIGH while input or output) can be read from the PINX registers. For actually setting the output state (or enabling/disabling the internal pullup resistor) the PORTX registers are used. For changing the direction of a pin between output and input, the DDRX registers are used (where X is the character of the port used). Every port is then represented by one byte in the corresponding SFR (1 bit per pin). The pins are organized in ports with 8 (or sometimes less) pins. In the end everything, that is done on a microcontroller, comes down to reading and writing Special Function Registers (SFR). Also there is a list of assembler command with descriptions. You can derive some of the program from there. Via google I found this series at github gist, which also has a blink example. You should start by looking into existing assembler blink programs. In this case you have to go the harder way. It will generate way more assembler code, than is really necessary for alternatively blinking two LEDs (for example digitalWrite() contains not only the actual writing to the corresponding pin registers, but much more code), and it will be obvious, that you didn't write it yourself. In the case, that this is a school assignment and you actually have to program directly in assembler, you probably don't want to directly convert your C++ sketch.
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